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Home , Properties of water, Water (data page)

OBSERVE THE UNIQUE PROPERTIES OF IN EVERYDAY LIFE

Answer Key and Teaching Notes

AUDIENCE To begin the activity, students are presented with the follow- ing summary of the . This activity is designed to be used during the first few weeks of the semester in a freshman-level introductory oceanogra- A. H2O form bonds with each other. phy class for nonscience majors, taught in a large (100+) lec- They arecohesive . ture hall format. B. H2O molecules like to bond with or other charged molecules. They areadhesive . ACTIVITY C. Because water bonds easily with other ions, it is the “uni- versal .” Format of Activity D. Water has a high specific . E. Water has a high heat of vaporization. This activity is designed to be formative assessment. Students F. Water’s greatest is at 4°C. Above or below that tem- work through scenarios of water behavior that they may have perature it becomes less dense. experienced in real life, making notes about why they chose G. Water has a low . the answers they did. The activity can be handed out as a work- sheet, or can be done one question at a time using PowerPoint. Scenarios The instructor then polls the class on each question, identi- fying and discussing common misconceptions. For scenar- Each scenario provides an opportunity to review one or more ios when more than one answer is correct, students give the basic property of water, an opportunity to identify and address answer they feel most sure about, followed up by identifying common misconceptions, and an opportunity to draw paral- other potential answers. The students correct their own work, lels between these scenarios and complex oceanographic phe- making notes about the explanations given by the instruc- nomena discussed later during the semester. tor. The entire activity is designed to fit into a 50-minute class window, with approximately 20–25 minutes each for student 1. It is a sweltering day at an outdoor concert. You group work and follow-up discussion as an entire class with walk through a misting booth, which sprays fine water the instructor. droplets onto you, and for a few minutes afterward you feel much cooler. A slide show and video covering the basic properties of water are available in the online supplemental materials and can be ANSWER: E. As the water evaporates, you feel cooler, because assigned for pre-class viewing. you are losing heat to the evaporating water. Some students may confuse the latent heat of vaporization with the closely As a follow up to the activity, when important oceanographic related, broader concept of specific heat, presenting an oppor- concepts center on understanding the properties of water, the tunity to review the two concepts and how they are related. instructor reminds students of these scenarios. Associating common, every day phenomena with more complex hydro- CONNECTIONS TO COURSE MATERIAL: When discuss- sphere/atmosphere/lithosphere interactions helps students ing the condensation of water droplets in ’s atmosphere, understand these concepts more fully. students can be reminded that this is the opposite process as described here and asked to predict how condensation would affect the of the surrounding atmosphere. 2. You’re on a road trip through the desert. You stay in CONNECTIONS TO COURSE MATERIAL: This is a helpful a hotel with a swimming pool. Even though it’s been analogy when discussing the formation of sea or the links scorching hot all day, you dive in without fear. between change, sea ice, and sea level.

ANSWER(S): D, E. Water has a high specific heat, and there- 6. You have a fishing pond full of catfish. The winter is fore it changes temperature very slowly. The water is cooler unusually cold and the pond over and stays that than the highest air temperature experienced during a given way all winter. The next spring the ice melts and the day, because it is subjected to these elevated for pond is still full of live fish. a limited time each day. Also E, because water is evaporating from the pool throughout the day, and the high latent heat of ANSWER(S): D, F. The pond never completely froze due to the vaporization leaves the water cooler. high specific heat of water. As the pond started to freeze, the less dense ice stayed at the top, insulating the rest of the water. CONNECTIONS TO COURSE MATERIAL: This analogy is use- ful when discussing the moderating effects of currents CONNECTIONS TO COURSE MATERIAL: This is a help- on coastal landmasses. ful analogy in understanding why the ocean does not com- pletely freeze, even in the . It is also helpful in 3. You go for a hike and decide to add a powdered understanding how life survives in the ocean, even in extreme drink to your water bottle. You sprinkle in the . powder and it quickly dissolves. 7. While sitting by the edge of a stream, you observe ANSWER(S): C, B that some insects can walk on the surface of the water without falling through. CONNECTIONS TO COURSE MATERIAL: Students can recall this phenomenon as they learn about the of ocean ANSWER(S): A. Although is not one of the water or try to understand how dissolved ions in the ocean choices on the list of water properties, students should under- originate from chemical on land, or the release of stand the underlying reason why water has surface tension, ions at mid-ocean ridge smokers. This analogy is also useful which is . when discussing the role of water in living things, and when discussing dissolved nutrients in . CONNECTIONS TO COURSE MATERIAL: This scenario is useful as a reminder of cohesion, and of surface tension when 4. In chemistry class, you pour water into a graduated discussing the phenomenon as a restoring force for waves. cylinder. You carefully take note of the meniscus that forms at the top. 8. You touch the edge of a paper towel to a puddle of water. Very quickly the paper towel absorbs the water. ANSWER: B. The meniscus forms because the water molecules are attracted to the cylinder, exhibiting . ANSWER(S): A, B. This occurrence is due to both adhesion and cohesion. Students are generally evenly split as to which is CONNECTIONS TO COURSE MATERIAL: When discuss- correct, with a few having determined that both are involved. ing benthic communities and infaunal habitats, adhesion is The absorption is the result of capillary action, a concept not important in understanding that seafloor sediment includes previously introduced. The instructor can take the opportu- seawater. Why is the sediment wet? Why is it mixed with sea- nity to introduce this new concept, or merely the students water? How can animals live in seafloor sediments? though understanding how the two can work together. The polar water easily adheres to other substances (mak- 5. An Arctic blast comes through town. The next day, ing them “wet”), and because water also is cohesive, the water the plumbers are busy as pipes burst all over town. molecules “pull” each other into the paper towel.

ANSWER(S): F. Although almost everyone has observed the CONNECTIONS TO COURSE MATERIAL: Capillary action is expansion of water when it freezes in everyday life, many how water and dissolved nutrients move within plant tissues. students seem conditioned to assume that are always Capillary action is also why water will absorb into even very denser than . fine sediments such as clay minerals. 9. You can’t get the last little bit of ketchup out of the POTENTIAL MODIFICATIONS TO ACTIVITY jar. You decide to add a little water to help. ONLINE: Because the questions are essentially multiple choice, ANSWER(S): B, C, G. Two obvious phenomena work together they could easily be used in an online course, with carefully in this situation. Like the energy drink powder, water, the uni- written feedback for right and wrong answers taking the place versal solvent, reacts quickly with compounds that make up of classroom discussion. ketchup, dissolving them. Viscosity plays a role here as well, as the low viscosity of water, compared to that of ketchup, enables CULTURAL: The scenarios were written for a student popula- that last little bit to escape from the jar. A third factor at work tion from a primarily rural or small-town background in the in this scenario is that the last little bit of ketchup is difficult to south. The scenarios could be rewritten to resonate more with get out of the jar partly because ketchup is a water-based sub- an urban population. For instance, instead of going for a hike, stance and therefore exhibits adhesion to the jar. When very the student who is mixing a powdered energy drink could be little ketchup is left, the force of the adhesion is stronger than engaged in a sports activity. The catfish pond could instead the force of gravity. A question for discussion is “What are we be a goldfish pond in the park. In warmer climates, the fro- trying to accomplish when we shake the ketchup jar?” zen pipes could be replaced with a soda put into the freezer and then forgotten. The scenarios could also be adapted to CONNECTIONS TO COURSE MATERIAL: The ability of water reflect life experiences common to specific underrepresented to dissolve and mix with ketchup is a useful analogy for dis- populations. cussing dissolved ions in ocean water. The addition of the ketchup to the water changes the water’s viscosity. This is a ACCESSIBILITY: If the class included students with visual useful concept to review when discussing density differences impairment, the scenarios could be rewritten to emphasize in water of various . non-visual interactions with water.

10. As raindrops fall on a surface, they quickly tend to form beads or drops.

ANSWER(S): A. As the raindrops land on the solid surface, the cohesion of the water molecules causes the drops to form. Students may also mention adhesion as being a reason the water droplets may stay in one place, even on a vertical sur- face. If students do not mention this, the question can be posed as to why this phenomenon occurs.

CONNECTIONS TO COURSE MATERIAL: Understanding the cohesiveness of water molecules helps explain the large amount of energy needed to cause water to evaporate into a .